After the Great Mississippi River flood of 1927, the US Army Corps of Engineers ramped up its efforts to contain the lower Mississippi. They built higher and deeper levees, along with flood control structures and spillways to relieve stress during high water events — it was one of the most ambitious engineering projects on Earth. And it largely worked, protecting river cities and keeping trade flowing. But with climate change, many people along the river worry about how much longer the intricate system can hold. The World’s Jason Margolis continues our special coverage of the Mississippi at a crossroads.